In practice, regulating circuits having actuating drives for flaps and valves in the field of HVAC continually begin to vibrate. A vibration of said type can be of short duration, for example during start-up, but also occurs because regulating circuits can never be set to be stable. This leads to an early failure of actuating drives, and the latter must be repaired or replaced before the expected service life has expired. It is therefore in the interests of suppliers and customers that early failures of said type are prevented.
In order that vibrations can occur, two conditions in particular must be met:                amplitude condition: the gain of the entire system must be at least equal to 1.        phase condition: there must be a time lag in the system which is sufficiently large.        
A vibration remains in the steady state if, in the case of a total gain of at least 1, the phase shift of the entire system is 360°.
The undesired vibrations can therefore differ not only in frequency but also in amplitude. If intense non-linearities are involved, as is the case for example with unfavorably-designed valves, a vibration can thus generally occur only in certain operating ranges of a system. Depending on this, the amplitude of a steady-state vibration can also be different. If a regulator is set in a grossly incorrect manner, a vibration can encompass the full range of an actuating signal until it is limited by the restricted output range of the regulator. In said limit case, the vibration can also be rectangular or approximately rectangular.
In U.S. Pat. No. 6,264,111 A, the gain of a regulator, the so-called P component, is adjusted. If the gain of the entire system, for example regulator, actuating member, air conditioning system, room and sensor, is small enough, then the vibration disappears. The means for suppressing the vibration are integrated directly in the regulator, and the input and output variables of the regulator are always known. It is possible using different means, also adaptive means, to suppress or eliminate vibrations, though it is in part necessary to accept significantly poorer regulating performance. Said degradation can be expressed for example in persistent temperature deviations or a very lethargic matching of the temperature.